1266 XANTHESTE HETEROXANTHINE. 



on the access of ammonia fumes. Carnine gives a similar 

 coloration if but little chlorine-water is used, while guanine 

 and adenine do not. 



ii. Hoppe-Seyler's reaction. When xanthine is introduced 

 into some caustic soda with which some chloride of lime lias 

 been mixed, each particle of the substance surrounds itself with 

 a dark green ring which speedily turns brown and then disap- 

 pears. 



iii. Strecker's test. When evaporated to dryness on porce- 

 lain with nitric acid a yellow residue is obtained which turns 

 reddish-yellow on the addition of caustic soda or potash (not 

 of ammonia) and reddish-violet on subsequent warming. Dis- 

 tinctive from uric acid. 



iv. Xanthine is more readily soluble in ammonia than is 

 uric acid. 



v. Xanthine yields in solution in dilute nitric acid a char- 

 acteristic crystalline compound with nitrate of silver, which 

 differs from the similar compound of hypoxanthine both in the 

 forms which it presents and in its greater solubility in nitric 

 acid of sp. gr. 1-1 at 100. It is therefore used as a means of 

 separating xanthine and hypoxanthine. 



FIG. 219. CRYSTALS OF XANTHINE SILVER-NITRATE, CsH^N^a . AgNOj. 



(Krukenberg after Kiihne.) 



vi. The compound of xanthine with hydrochloric acid is 

 far less soluble in water than are the similar compounds of 

 hypoxanthine and guanine, and hence affords a further means 

 of separating these bases. 



2. Heteroxanthine. C 6 H 6 N 4 O 2 . (Methyl-xanthine.) 



This substance occurs in minute quantities in the normal 

 urine of man and the dog, along with xanthine and hypoxan- 

 thine and another closely allied xanthine base, paraxanthine. 

 It occurs in larger amount in the urine of leukhtemic patients. 

 It is crystalline, but not very characteristically so, is soluble 

 with difficulty in cold water, much more soluble in hot water, 

 is insoluble in alcohol and in ether. It may, as also may 

 paraxanthine, be separated from other xanthine bases by taking 

 advantage of the relatively slight solubility of its sodium salt 



